1. Field of the Invention
The present invention relates to a real-time ultrasonic diagnostic apparatus and ultrasonic diagnostic apparatus and system using an ultrasonic probe that is to obtain in real time an image in a living body while scanning with an ultrasonic beam, and more particularly to an ultrasonic diagnostic apparatus using a probe incorporating an electronic circuit therein.
2. Description of the Related Art
Recently, the ultrasonic two-dimensional (2D) array probe, etc. tend to incorporate an electronic circuit in the probe head thereof, to generate a transmission waveform and amplify/partially beam-form the resulting reception echo. For example, JP-A-2000-139907 describes an ultrasonic diagnostic apparatus using such a two-dimensional array probe.
Meanwhile, it can be considered to use a stack of piezoelectric elements, etc. in order to suppress the impedance increase resulting from the miniaturization of vibrator elements.
For example, in the real-time ultrasonic diagnostic apparatus using a probe incorporating an electronic circuit, its probe handle is made up with an ultrasonic vibrator group, a pulser group, a preamplifier group, a sub-array beam former group, and a control circuit for controlling those. Meanwhile, an ultrasonic probe is constituted by the probe handle together with a probe cable, a probe connector and an electronic circuit group and an in-probe-connector control circuit.
Meanwhile, in the ultrasonic diagnostic apparatus body to which the ultrasonic probe is connected through the probe connector, amplification is made on the ultrasonic echo signals subjected to reception-delay addition at the in-body amplifier group. The amplified ultrasonic echo signals are matched in timing together at a reception-delay addition circuit and then detected at a signal processing section, to be extracted of an envelope. This is transformed in coordinate at the image processing section and processed suitably for image display, thus being displayed on a display section. This allows for displaying the subject as shape information in a real time.
In the meanwhile, by transmitting and receiving an ultrasonic wave at a center frequency f0 to and from the blood flowing through the subject, an ultrasonic beam having a frequency f0+fd is received by means of the moving corpuscles through the action of a Doppler shift fd proportional to the blood velocity. For this reason, by detecting the Doppler shift frequency fd and displaying a change in time thereof, blood-velocity information is to be displayed as a Doppler image.
In such a case, by two-dimensionally mapping the detected Doppler shift frequencies fd and displaying those over the ultrasonic image through proper color change, the image of the subject can be displayed in real time as a color Doppler image (not shown) including blood velocity information.
The ultrasonic probe recently uses a two-dimensional array of vibrators wherein the number of vibrators amounts to several thousands while reduced in their individual sizes. In such a case, if connecting the probe directly to the ultrasonic diagnostic apparatus, there is a need of increasing number of cables. This however increases cable thickness and hence raises troublesomeness upon handling. Moreover, there encounters a difficulty in delivering a drive waveform to the precise vibrators with efficiency and in conveying an ultrasonic echo, received at the precise vibrators, with quality.
Consequently, for two-dimensional array or the like, the ultrasonic probe is mounted with an electronic circuit including transmission and reception circuits. In addition, it is an often practice to reduce the number of input signal lines to the ultrasonic diagnostic apparatus by driving a number of precise vibrators with easiness and efficiency, amplifying a received weak ultrasonic echo with efficiency and summing up the values through partial reception-beam forming as to several vibrators a time.
However, there is a need to reduce the heat generation at the electronic circuit incorporated in the probe, in order to suppress the temperature rise of the ultrasonic probe within a permissible level. Consequently, there is a problem that the power, to be supplied to the incorporated electronic circuit, could not be increased. Meanwhile, as for the preamplifier group for ultrasonic-echo amplification, FETs (field-effect transistors) in most cases are used as representative amplification elements. The FET preamplifier requires a greater amount of bias current as shown in FIG. 1, in order to obtain a broad dynamic range at low noise.
The FET M1 has a noise-in-input (thermal noise) that is to be determined as in the following.vn=4kT(2/3)·(1/gm)gm=2·ID/(VGS−VTH)
Accordingly, the bias-current must be increased for reducing the noise.
Namely, in order to amplify an extremely weak Doppler signal superposed on a great-amplitude clutter (reflection of from heart wall, etc.) as in a continuous wave Doppler (SCW) mode, there is a need to supply a significantly great bias current that is nearly double the bias current for obtaining the usual B-mode image.
As a result, heat generation increases on the preamplifiers to increase the probe temperature, thus resulting in excessive heat generation and possible improper operation of the incorporated electronic circuit. In case the bias current is used suppressively in order to avoid it, dynamic range is not fully obtained as to the preamplifiers. This makes it difficult to amplify a weak signal component with fidelity, thus making it impossible to obtain information to a diagnostically required extent.